28-11-2015, 05:49 PM
Given that someone in a recent post mentioned a dearth of restoration stories, I thought I’d add one, not that it’s anything to shout about, but might be of interest.
I’ve just finished restoring a KB FB10 MK1 - one of three sets I bought for a fiver each off the BVWS stall at the Golborne swapmeet recently. It had a chunk out of the cabinet at the rear and was a bit scruffy and tired looking, with a faded speaker cloth. Nevertheless, it was well worth a fiver! It was missing a 6BA6 valve, a 6BE6 when tested had an open circuit heater, and the mains switch on the pot was open circuit.
I’ve restored several of these little sets, which I rather like. I’ve restored two for my son – one with a nice undamaged cabinet which polished up nicely, another which had a damaged cabinet, which at my sons request, I sprayed green. I’d also restored another for myself which had a damaged cabinet, and I re-sprayed that one red. My son asked if I came across one in need of TLC, if I’d spray it red for him, so the one I bought at Golborne was a good candidate.
The others had been MK2 sets, which have a different valve line-up (6BE6, 6BJ6, 6AT6, 6BW6 & 6V4), whereas the MK1 has a mixture of B7G valves and Octal. (6BE6, 6BA6, 6AT6, 6V6GT & 6X5. The MK1 has a frame aerial, whereas the MK2 has a ferrite rod. There are other differences – notably in the power supply, and with the trimmers. In the MK1, there appears to be no trimmers – just bits of wire which appear to have been soldered to the tuning cap gangs and snipped off. That’s actually what they are – bits of twisted wire, trimmed to length at the factory as rudimentary trimmers, which are not adjustable. On the MK2 the trimmers as I recall are adjustable ‘postage stamp’ types.
Both the MK1 & MK2 have what appear to be a mains transformer, which it is of course, but they’re auto transformers with only a tapped primary to feed the valve heaters and dial light. Hence, the AC feed to the rectifier comes directly off the mains to the anodes of the rectifier (both strapped together), via a 150R 7 Watt resistor, and one side of the set is connected to the chassis, so polarity is important and the usual ‘live chassis’ precautions are called for. (I use a mains isolating transformer when doing live trusting on AC/DC sets and sets which lack a full mains transformer, and carry out as much testing as I can with the set disconnected from the mains – too young to die – too old for nasty shocks!).
The HT feed is a bit peculiar in that it uses two 8K2 resistors in parallel, making 4K1, then a 1K8 resistor in series, totalling 5K9. Either a single 5k6 or 6k2 preferred value resistor would have been 5% over/under and I’d have thought would have been fine. Seems odd to have used three resistors where one would do, in such a compact set. No matter.
First off I decided to repair and re-spray the cabinet, which had a chunk out of the rear at the bottom. I bridged the gap with thick gauge paper clip wire to form and armature to support the filler, drilling sideways into the edges of the cabinet. I wrapped thin copper wire over the two pieces of paper clip, and then bridged the gap with Isopon body filler. I cut a template from the undamaged part of the back and used that as a guide to shape the repaired portion. When sanded to shape, primed and finished with gloss, the repair is invisible. The old speaker cloth was badly faded and in any event, not a suitable colour, so I found a piece which went well with red and used that.
Wit the cabinet sorted, I turned to the chassis, and as I always do on any set, the first task was to make a little cradle to support the chassis to do the restoration work and tests – in this case, just a piece of scrap ply and two brackets made of 1” wide flat steel strip.. I can’t for the life of me understand why anyone attempts work on any set without properly supporting it. Not only does it make life difficult, it risks damaging valves etc. When service engineers used to repair sets in customer’s homes, they were up against time pressures and often had the set on the floor, sat crossed-legged, and had perhaps half an hour before they had to be off to the next job. Also, they were only doing one-off repairs to get the set going again – they were not carrying out restorations which may take many hours over a period of several days. We’re not under those time pressures, so why cut corners? I have a chum who used to work for Radio Rentals. He tells me that they were expected to repair 14 – 16 TV sets a day and often didn’t have time to let his soldering iron warm up, so he just twisted wires together when possible, unless it was on a PCB.
Having popped the chassis on a cradle, I checked the resistors to see if any were more than 20% out of spec. Most were still well within that and only two needed changing as they were 60% high. I changed the seven waxy paper caps, though when I tested the old ones out of curiosity at 500V on my Victor VC60B insulation tester, no showed any sign of leakage. The twin 32uF smoothing cap wouldn’t reform, so I stuffed the old can with two new caps, which just fitted. On the pic of the guts of the old one will be seen an elastic band from when it was made. It was still intact!
I was expecting to have to replace the volume control due to the open circuit on/off switch and had a switched 470k log pot to hand. However, a good squirt of Servisol into the switch section did the trick – at least for now. The wires to the dial light, which traverses back and forth along the dial, were brittle so I changed those and another dodgy bit of wire. I had to re-string the dial, which - though not complex is vey fiddly and would test the patience of a saint. They must have had deft fingers on the production line and no doubt did it in a jiffy, day in day out!
I popped in two replacement valves and switched on the set via a lamp limiter – silence – not a peep. Audio stage was fine, IF too - 422kHz, sot on. Hence, trouble in the front end. Turned the lights off in the workshop - not a glimmer from the NOS 6BE6 frequency changer valve I’d fitted. Lights back on, I removed it and checked the filament, which was fine. Popped the DMM test prods into the valve socket to check for 6V3 AC – nothing there. Took a close look under the chassis at the heater line and noted that the connection to the valve-holder had fractured. I soldered that back on and the set came to life on MW & LW. Checked the Voltages around the set and all were fairly close to spec. Before I put the cabinet on, I checked all the valves on my Taylor 45D and they tested like new.
Handed the set to my son to add to his small collection, who is very pleased with it.
A few pics attached.
Hope it's of interest to someone out there.
I’ve just finished restoring a KB FB10 MK1 - one of three sets I bought for a fiver each off the BVWS stall at the Golborne swapmeet recently. It had a chunk out of the cabinet at the rear and was a bit scruffy and tired looking, with a faded speaker cloth. Nevertheless, it was well worth a fiver! It was missing a 6BA6 valve, a 6BE6 when tested had an open circuit heater, and the mains switch on the pot was open circuit.
I’ve restored several of these little sets, which I rather like. I’ve restored two for my son – one with a nice undamaged cabinet which polished up nicely, another which had a damaged cabinet, which at my sons request, I sprayed green. I’d also restored another for myself which had a damaged cabinet, and I re-sprayed that one red. My son asked if I came across one in need of TLC, if I’d spray it red for him, so the one I bought at Golborne was a good candidate.
The others had been MK2 sets, which have a different valve line-up (6BE6, 6BJ6, 6AT6, 6BW6 & 6V4), whereas the MK1 has a mixture of B7G valves and Octal. (6BE6, 6BA6, 6AT6, 6V6GT & 6X5. The MK1 has a frame aerial, whereas the MK2 has a ferrite rod. There are other differences – notably in the power supply, and with the trimmers. In the MK1, there appears to be no trimmers – just bits of wire which appear to have been soldered to the tuning cap gangs and snipped off. That’s actually what they are – bits of twisted wire, trimmed to length at the factory as rudimentary trimmers, which are not adjustable. On the MK2 the trimmers as I recall are adjustable ‘postage stamp’ types.
Both the MK1 & MK2 have what appear to be a mains transformer, which it is of course, but they’re auto transformers with only a tapped primary to feed the valve heaters and dial light. Hence, the AC feed to the rectifier comes directly off the mains to the anodes of the rectifier (both strapped together), via a 150R 7 Watt resistor, and one side of the set is connected to the chassis, so polarity is important and the usual ‘live chassis’ precautions are called for. (I use a mains isolating transformer when doing live trusting on AC/DC sets and sets which lack a full mains transformer, and carry out as much testing as I can with the set disconnected from the mains – too young to die – too old for nasty shocks!).
The HT feed is a bit peculiar in that it uses two 8K2 resistors in parallel, making 4K1, then a 1K8 resistor in series, totalling 5K9. Either a single 5k6 or 6k2 preferred value resistor would have been 5% over/under and I’d have thought would have been fine. Seems odd to have used three resistors where one would do, in such a compact set. No matter.
First off I decided to repair and re-spray the cabinet, which had a chunk out of the rear at the bottom. I bridged the gap with thick gauge paper clip wire to form and armature to support the filler, drilling sideways into the edges of the cabinet. I wrapped thin copper wire over the two pieces of paper clip, and then bridged the gap with Isopon body filler. I cut a template from the undamaged part of the back and used that as a guide to shape the repaired portion. When sanded to shape, primed and finished with gloss, the repair is invisible. The old speaker cloth was badly faded and in any event, not a suitable colour, so I found a piece which went well with red and used that.
Wit the cabinet sorted, I turned to the chassis, and as I always do on any set, the first task was to make a little cradle to support the chassis to do the restoration work and tests – in this case, just a piece of scrap ply and two brackets made of 1” wide flat steel strip.. I can’t for the life of me understand why anyone attempts work on any set without properly supporting it. Not only does it make life difficult, it risks damaging valves etc. When service engineers used to repair sets in customer’s homes, they were up against time pressures and often had the set on the floor, sat crossed-legged, and had perhaps half an hour before they had to be off to the next job. Also, they were only doing one-off repairs to get the set going again – they were not carrying out restorations which may take many hours over a period of several days. We’re not under those time pressures, so why cut corners? I have a chum who used to work for Radio Rentals. He tells me that they were expected to repair 14 – 16 TV sets a day and often didn’t have time to let his soldering iron warm up, so he just twisted wires together when possible, unless it was on a PCB.
Having popped the chassis on a cradle, I checked the resistors to see if any were more than 20% out of spec. Most were still well within that and only two needed changing as they were 60% high. I changed the seven waxy paper caps, though when I tested the old ones out of curiosity at 500V on my Victor VC60B insulation tester, no showed any sign of leakage. The twin 32uF smoothing cap wouldn’t reform, so I stuffed the old can with two new caps, which just fitted. On the pic of the guts of the old one will be seen an elastic band from when it was made. It was still intact!
I was expecting to have to replace the volume control due to the open circuit on/off switch and had a switched 470k log pot to hand. However, a good squirt of Servisol into the switch section did the trick – at least for now. The wires to the dial light, which traverses back and forth along the dial, were brittle so I changed those and another dodgy bit of wire. I had to re-string the dial, which - though not complex is vey fiddly and would test the patience of a saint. They must have had deft fingers on the production line and no doubt did it in a jiffy, day in day out!
I popped in two replacement valves and switched on the set via a lamp limiter – silence – not a peep. Audio stage was fine, IF too - 422kHz, sot on. Hence, trouble in the front end. Turned the lights off in the workshop - not a glimmer from the NOS 6BE6 frequency changer valve I’d fitted. Lights back on, I removed it and checked the filament, which was fine. Popped the DMM test prods into the valve socket to check for 6V3 AC – nothing there. Took a close look under the chassis at the heater line and noted that the connection to the valve-holder had fractured. I soldered that back on and the set came to life on MW & LW. Checked the Voltages around the set and all were fairly close to spec. Before I put the cabinet on, I checked all the valves on my Taylor 45D and they tested like new.
Handed the set to my son to add to his small collection, who is very pleased with it.
A few pics attached.
Hope it's of interest to someone out there.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
